1. Field of the Invention
The present invention relates to a pattern forming method to form a desired pattern on a substrate to be processed. The present invention relates to a mask manufacturing method to manufacture a mask based on a corrected pattern, especially. In addition, the present invention relates to an LSI manufacturing method to form an LSI pattern on a wafer based on a mask to which a pattern is corrected.
2. Description of the Related Art
In manufacture of an LSI, first, a mask having an opening or a light shielding pattern which corresponds to an LSI pattern using a mask drawing device etc. is manufactured. Next, the pattern on the mask is transferred to a resist on the wafer using an optical stepper or a scanner. Thereafter, a pattern of one layer is manufactured through various processes such as development and etching. The LSI is manufactured repeating such a pattern manufacturing process. In manufacture of the mask, the mask is manufactured through some processes of exposure of the resist on the mask with the mask drawing device, development of the resist and etching of a COG (Cr On Glass) etc.
The electron beam exposure device is chiefly used for drawing of the mask now, but the light might be used. The light is used in general in the device which transfers the pattern on the mask to the wafer, and the technology which uses an electronic line and X rays is also studied. Even in the pattern formation for only one layer of the LSI, various processes as mentioned above are required in any one of techniques.
In the LSI pattern or the pattern on the mask made through such processes, there are the following problems. This problem is a problem that “each pattern is almost uniformly finished (Locally, the difference with the design size is almost the same) at local observation, but the pattern size gradually changes if it is observed with in all internal of the chip formed in the entire mask or the wafer (The difference with the design size changes gradually in the chip)”.
This appearance is shown in FIG. 1 schematically. The difference with the design size is small at the near position in the wafer chip (local). However, the difference with the design size is large at the point of far position in the chip (wide range). Here, the distribution of the error shown in FIG. 1 becomes the distribution of which the size error depending on the pattern and the size error depending on the position shown in FIG. 2A to FIG. 2C are added. FIG. 2A shows the line & space pattern. FIG. 2B shows the size change according to the pattern density. FIG. 2C shows the size change in two-dimensional plane position.
As a similar problem, there is an effect which is called a “Fogging” occurred when the mask drawing is performed with the electron beam exposure device. The fogging is the effect that the resist on the mask is exposed, thereafter the electron rebounds on the substrate, returns to the upper part of the stage of the device, reflects again thereby, and exposes the resist. The result brought about in this effect is similar to a wide range size changing as mentioned above, and the size changes gradually by the level of several cm. Therefore, the “Fogging” effect is one of wide range pattern size degradation factors on the mask.
The technology which adjusts the dose for each place is proposed as an action plan to the problem of this “Fogging” (fogging correction). In this method, the dose in each place to correct the size change is obtained with the computer etc. beforehand. The fogging effect is corrected (accurately controlled) by changing the dose based on it. Here, the dose is calculated as follows. The mask is divided into small areas, and the density of the pattern therein is calculated. Then, the calculated result is used. However, the technique of this fogging correction does not become an enough solution means to the problem of a wide range size change as follows.
First of all, this method is a method only to correct the fogging for the mask drawing with the electron beam exposure device. That is, it is a method of controlling the variation of an effective dose. Therefore, since the wide range size error which occurs on the process cannot be corrected, if this is done forcibly, the accuracy of the proximity effect correction etc. is degraded.
Therefore, it is insufficient to apply this method as it is when the LSI pattern is formed on the wafer, and the error caused by the etching when the reticle is made is corrected.
The second problem includes a problem on accuracy and the calculation time. There are other size degradation factors called as a proximity effect besides the fogging effect in the electron beam exposure device. This is a comparatively local size degradation factor to exert the influence on the area of about 30 μm. Since the size error occurred thereat is about 100 nm, and it is farther larger than the above-mentioned wide range size change. When this proximity effect is corrected, the method of changing the dose for every place is used.
In a word, both the fogging correction and the proximity effect correction adopt a method of changing the dose of each place to perform the correction. Therefore, to perform the correction processing accurately to all errors, it is necessary to calculate the optimal dose by considering both of them at the same time. To execute the method, it is necessary to calculate the optimal dose for each area (for instance, 1 μm×1 μm), which is farther smaller than the range where the proximity effect correction exerts. Additionally, it is necessary to consider all the influences of the pattern of the range that the influence of the fogging is exerted (for instance, several cm square).
The optimal dose is calculated by using a special circuit only in a case of the proximity effect correction now. The time required to calculate the optimal dose is about one hour. On the other hand, the distance to which the influence of the fogging is exerted is 30 times or more the distance to which the influence of the proximity effect is exerted. Since the amount of the calculation and the calculation time are proportional to the square of the area, about 1000 times the calculation time are required as assumed to be 30×30 times. That is, to calculate the fogging correction of the proximity effect correction at the same time, even if the special circuit can be used to correct the proximity effect now, the time becomes extending over about 1000 hours ,that is, about two months.
Therefore, the following methods have been adopted as a method of a conventional fogging correction. In the fogging correction, the dose is calculated only from the density of the pattern by ignoring the result of the proximity effect correction. The dose is calculated by performing real time processing in the drawing device by ignoring the influence of the fogging in the proximity effect correction. The dose for the fogging correction and the dose of the proximity effect correction are combined, a final dose is calculated, and the correction is performed. Since the interrelationship and the dependency between the proximity effect correction and the fogging correction will be ignored, when such a method is used. As a result, the error is caused. Therefore, the error occurs in the fogging correction, and in the effect on a wide range size change, the error is controlled to ¼ as far as possible. With this, the accuracy needed now and in the future cannot be satisfied.
Two or more processes and two or more manufacturing devices are needed in conventional manufacture of the mask and the LSI like this. It cannot be avoided to occur the wide range size change caused by this. And, it is difficult to accurately correct the wide range size change.